Sean Wilentz is a history professor at Princeton and the author of “The Rise of American Democracy: Jefferson to Lincoln,” a celebrated exploration of the early Republic. He is also an avowed partisan in a classic American struggle, which is to say he’s a Yankees fan who has had season tickets for more than three decades. 

Wilentz was at Yankee Stadium in 1961 when Roger Maris hit his 61st home run. He remains devoted and passionate. So in the fall of 2013, when a talented Princeton baseball player named Mike Ford needed an adviser for his senior thesis, Wilentz thought it could be a match. 

Ford was the reigning player and pitcher of the year in the Ivy League. Wilentz was a faculty liaison for the Tigers’ baseball program. And Ford, a history major, had already taken Wilentz’s lecture class on America from the Revolution to the Civil War. “He did pretty well, as I remember,” Wilentz said.